1. Field of the Invention
The present invention relates to a radio communication system and more particularly, to a mobile radio communication system that enables to reduce power consumption during a standby time for waiting a call from a base radio station without reception performance deterioration.
2. Description of the Prior Art
Conventionally, to reduce power consumption of a mobile radio communication system during a standby time, it has been well known that a radio receiver block of the system is controlled to be active intermittently, reducing the effective consumption power. With this method, for example, a control block of the system feeds a signal into a power-supply controller circuit of the system at specified intervals so that the receiver block becomes active or inactive in response to the signal.
With this conventional method, however, some control protocol is required in advance to communicate between the system and any base station. If the system operates without the protocol, there is a possibility that it fails to receive necessary signals from the base station.
To solve this problem, other methods have been developed under the estimate or expectation that slight sensitivity reduction of the radio receiver does not cause any problem. An example of the methods is disclosed in the Japanese Non-Examined Patent Publication No. 57-33846 (published in February 1982), in which the sensitivity of the radio receiver block is reduced during a standby time and is returned to the original or normal value at the time of reception of a calling signal, resulting in reduction of power consumption.
During the standby time, a radio wave intercepted by an antenna is supplied to a radio receiver circuit through a radio-frequency (RF) attenuator. An input level of the receiver circuit is reduced by the attenuator. Consequently, only a strong radio wave transmitted from a specific area is detected and the other weak radio waves having the same frequency as the strong radio wave are not detected. A detector circuit detects the output of the receiver circuit and judges whether the demodulated output contains a call signal for the radio receiver or not.
When the call signal is received, the radio wave intercepted by the antenna is supplied to the radio receiver circuit without passing through the attenuator, maximizing the sensitivity of the receiver circuit. The demodulated output of the receiver circuit is supplied to an audio-freqency (AF) amplifier. Thus, the amplified output of the AF amplifier drives a speaker.
Another example of the methods is disclosed in the Japanese Non-Examined Patent Publication No. 63-13525 (published in January, 1988), in which a supply current to a receiver block is reduced under the condition that the receiver block has a sensitivity suafficient to detect a wanted RF signal, resulting in reduction of power consumption.
A RF signal intercepted by an antenna is supplied to a radio receiver block through a duplexer. The receiver block contains a RF amplifier, a frequency converter, an intermediate-frequency (IF) amplifier, and an AF amplifier. The AF amplifier has a demodulator and a noise or electric-field sqelch circuit.
A part of the output of the receiver block, which changes dependent on whether any RF signal is contained therein, is supplied to a main controller. As a part of the output, an output of the noise or electric-field squelch circuit is used typically. Another pert thereof, which is a voice signal containing a call signal or the like, is supplied to a current controller for controlling a supply current to the receiver block. The main controller controls a radio transmitter block. The main controller controls the receiver block also through the current controller.
The transmitter block supplies a RF output signal to the antenna through the duplexer under the control of the main controller.
A power supply, which is typically made by a dry or storage battery or batteries, supplies a power to the main controller, the transmitter block and the current controller.
Since no RF signal is supplied to the receiver block during a standby time, the current controller reduces the supply current to the receiver block under the condition that the receiver block has a sensitivity sufficient to be able to detect a wanted RF signal to drive the squelch circuit.
Even if the supply current to the receiver block is reduced, the sensitivity of the receiver block does not tend to decrease so much. This means that such the supply current reduction of the block causes no problem for detecting the wanted RF signal.
When any wanted RF signal is intercepted by the antena,the receiver block sends a signal to the current controller, so that the controller increases the supply current to the receiver block in response to this signal. Thus, the receiver block stares its normal operation.
For the above conventional methods in which power consumption reduction is realized by the sensitivity reduction of the radio receiver during the standby time, it is important to know the level to which the sensitivity can be lowered. This level is not disclosed clearly nor specifically in the method of the Japanese Non-Examined Patent Publication No. 57-33846.
In the method of the Japanese Non-Examined Patent Publication No. 63-13525 also, this sensitivity level is not shown clearly nor specifically. In view of this, the power consumption reduction is obliged to be performed without precise estimate of the sensitivity level. As a result, there arises a possibility that any RF signal transmitted from a base station fails to be received due to power consumption reduction. Alternatively, the sensitivity reduction is restrained because the reception of the RF signal is regarded as important, resulting in insufficient or no power consumption reduction.
Further, if the power consumption reduction is excessively progressed according to the above conventional methods, there arises a danger that the performance of the communication system deteriorates instead, degrading the marketability of the system.